What a pump actually does is move a column of water to create a flow. Pressure results from a restriction on than column of water as is the case when the water passes through a nozzle. When we speak of a pump’s ability to create a certain pressure at a certain flow, what we really mean is that the pump is capable of moving that amount of water per minute through a nozzle or restriction which actually creates the specified pressure.
In order to create a flow of water, most pumps used in the pressure cleaning industry rely on a system of valves and cylinders. The movement of a plunger or piston in the cylinder draws water through the inlet valve and the upstroke expels it through the outlet valve. The valves basically direct the water through the pump by preventing backflow.
The simplest valve design consist of a spring and poppet and is hydraulically operated by differences in pressure on either side of the valve. When pressure against the valve exceeds the ability of the spring to hold the poppet closed, the valve opens. On the opposite stroke, water itself presses the poppet against its seat, holding the valve closed and preventing flow of the water in the wrong direction.
The flow of water through the pump can be controlled in three ways, by increasing or decreasing the bore of the cylinder, by lengthening or shortening the stroke of the piston or plunger or by increasing or decreasing the speed at which the pump operates. ~ A-R North America
The above information is relevent to all pressure washer pumps manufactured by A-R North America, General Pump, Comet Pump, Giant Pump, Udor Pump, Hawk Pump, Landa Pumps, Mi-T-M Pumps, Hydor Tek Pumps, Pressure Pro Pumps, Allison Severe Duty Pumps and other pumps found on equipment utilized by professional mobile pressure washers.